The present invention relates to optical recording media and, in particular, to a manufacturing method for a disk-shaped optical recording medium having a recording layer which forms thereon local projections in response to radiation of laser beam.
Recently, considerable effort has been given to the development of optical recording media. Such recording media offer an advantage over other kinds of recording media in that they can store data information at high recording density to provide very large storage capacities.
There is known among those skilled in the art an optical disk having a recording layer made of an organic matrix which contains metallic clusters. When a write laser beam is radiated onto the recording layer, the metallic clusters absorb beam energy, and the matrix emits a gas contained therein to thereby form protuberances on the surface of the recording layer, whereby optical data may be stored in the optical disk.
The structure of the recording layer is simplified to improve the utilization efficiency of the laser beam. However, it is very difficult to properly control the relationship between the energy intensity of the laser beam and the amount of gas released from the organic matrix, thereby decreasing productivity of such optical disks. For example, when the energy intensity of the write beam is too high, the recording layer immediately bursts. Alternatively, when the beam intensity is too low, the production of gas from the matrix layer is insufficient to result in proper projection of the recording layer. An optimal (allowable) range of the beam intensity is thus narrowed. The amount of gas released from the recording layer also depends upon the ratio of the organic matrix to the metallic clusters. Accordingly, it is difficult to determine an optimal beam intensity. In order to perform proper data recording, a strict relationship between the ratio of the organic matrix to the metallic clusters in the recording layer and the laser beam intensity must be established. When the manufacturing process control is restricted to obtain the required ratio, the yield of the disks may be limited, i.e., productivity may be lowered, resulting in high cost. The drawback of the conventional optical disk of the above kind is due to insufficient thermal stability of the organic matrix.
There has been proposed in U.S. patent application Ser. No. 778,245 an improved optical disk free from the aforementioned drawbacks. This optical disk has a specific recording layer made of a refractory base layer in which metal clusters and organic clusters are uniformly contained. When a write laser beam modulated to represent data information is incident on the recording layer, the metal clusters absorb beam energy, the organic clusters produce a gas component, thereby causing the base layer to incur a local projection by a pressure of the gas component such that protuberances are formed on the recording layer.
In the above-identified Application for Patent, to manufacture the optical disk of the above structure, sputtering technique is used to form such recording layer on a substrate. According to this manufacturing method, however, a complexed target body having a backing plate on which pellets are provided. Since the number of pellets should be determined in accordance with desired contents of metal and organic clusters, different target bodies must be prepared to manufacture optical disks of different mixture ratios of such clusters. This may be a bar for optical disk manufactures to improve the productivity of optical disks.